1. Field of the Invention
This invention relates to the field of copolymers of ethylene, vinyl acetate and carbon monoxide, and more particularly, to processes for preparing such copolymers.
2. Description of the Prior Art
U.S. Pat. No. 3,780,140 describes the preparation of copolymers consisting essentially of by weight (a) 40-80% ethylene, (b) 3-30% carbon monoxide, and (c) 5-60% of one or more termonomers copolymerizable therewith, preferably vinyl acetate. The preferred copolymers include those consisting essentially of 56-76% ethylene, 3-15% carbon monoxide, and 10-34% termonomer. The copolymers are said to have a melt index normally within the range of 0.1-3000, and preferably 1-500. Blends of these copolymers with other polymers such as polyvinyl chloride and wax are also described. Where the polymer to be blended with the copolymers is wax, the preferred copolymer contains no more than about 5% carbon monoxide, and when the termonomer is vinyl acetate, 10-26% vinyl acetate is preferred (col. 2, lines 26 to 51). The flow of ethylene, carbon monoxide, monomers and catalyst into the polymerization reactor is controlled so that the monomers enter the reactor in continuous molar ratios and at the same rate at which product and unreacted monomers are discharged from the reactor. The reactor temperature should be at least 140.degree. C. (284.degree. F.), preferably 155-300.degree. C. (311-571.degree. F.) and most preferably 155-225.degree. C. (311-437.degree. F.), and the reactor pressure should be maintained within the range 5000-60,000 p.s.i., preferably about 20,000-35,000 p.s.i. (col. 3, lines 28 to 45). The data in this patent show no consistent or predictable relationship between polymerization temperature and melt index, the latter being a factor directly related to Melt Flow Rate (MFR).
U.S. Pat. No. 3,334,081 describes a process for polymerizing ethylene in a tubular reactor in the presence of a chain transfer agent at from 15,000 p.s.i.g. to about 100,000 p.s.i.g. and at a temperature of from about 90.degree. C. to about 350.degree. C. (194 to 662.degree. F.). The process is also applicable to the copolymerization of ethylene with numerous ethylenically unsaturated monomers, vinyl acetate among them. The patent also discloses that the process can be used to produce copolymers of ethylene with carbon monoxide in which the carbon monoxide charged can vary from 0.1 to about 20 mole percent of the total flow of ethylene to the reactor. U.S. Pat. No. 3,334,081 fails to disclose any terpolymer of ethylene, vinyl acetate and carbon monoxide.
U.S. Pat. No. 3,153,029 describes copolymers of ethylene and vinyl acetate or carbon monoxide modified with a terminating agent, among which are included carbon monoxide. There is no disclosure in this patent of reacting ethylene monomer and vinyl acetate monomer with carbon monoxide.
U.S. Pat. No. 2,702,794 discloses the emulsion copolymerization of ethylene and vinyl acetate at temperatures of from -50 to 125.degree. C. (-58 to 257.degree. F.). Other polymerizable monomers can be added as third components in minor amounts such as carbon monoxide, maleic anhydride, allyl glycidyl ether, methyl hydrogen maleate, maleimide, sulfur dioxide, vinyl chloride and acrylate and methacrylate esters. There is nothing in U.S. Pat. No. 2,702,794 which points to any advantage in copolymerizing ethylene, vinyl acetate and carbon monoxide.
U.S. Pat. No. 2,495,286 describes the copolymerization of carbon monoxide and an ethylenically unsaturated comonomer such as ethylene, with other comonomers such as vinyl acetate. Polymerization is carried out at from 25.degree. C. to as high as 350.degree. C. (77.degree. F. to as high as 662.degree. F.). Example 15 of the patent is illustrative of the preparation of a copolymer of carbon monoxide, ethylene and vinyl acetate. As discovered herein, the carbon monoxide content of the terpolymer is, at 37%, far higher than the maximum tolerable amount for a copolymer demonstrating improved MFR.